Display apparatus using oxide semiconductor and production thereof

ABSTRACT

A transistor includes a source terminal and a drain terminal, an active layer including an oxide containing In, a gate electrode, and a gate insulating layer between the gate electrode and the active layer. At least a part of the active layer is amorphous, and an electric current flowing between the source terminal and the drain terminal of the transistor is less than 10 μA when the transistor is in an off state. In addition, the gate insulating layer contains hydrogen in an amount of less than 3×10 21  atoms/cm 3 .

TECHNICAL FIELD

The present invention relates to a display apparatus using an oxidesemiconductor and a production method thereof, and in particular,relates to a top-emission type, bottom-emission type or two-sidedemitting type organic electroluminescent display apparatus or inorganicelectroluminescent display apparatus.

BACKGROUND ART

ITO (Indium Tin oxide) has been used for a transparent electrode in atransmission type liquid crystal device. However, since In₂O₃ of a mainraw material of ITO contains a rare metal, and it has been fearedwhether a desired amount of ITO can also be steadily supplied in future.Japanese Patent Application Laid-Open No. 2000-044236 proposes a methodof producing a new transparent conductor material which has a reducedcontent of In₂O₃, has a low electrical resistance, has an opticalabsorption edge in ultraviolet region and has an excellent blue lighttransmissivity; and an electrode material using the material.

In addition, materials which can be substituted for ITO have beenactively researched and developed. For instance, Japanese PatentApplication Laid-Open No. H07-235219 proposes a film of zinc oxide (ZnO)and a zinc-indium-based oxide. In addition, Japanese Patent ApplicationLaid-Open No. 2000-044236 proposes an oxide containing zinc-indium-basedoxide and a specified amount of an additive such as gallium.

In addition, there has been an attempt in recent years in which not onlyan electrode but also a channel layer (hereinafter, also referred to as“active layer”) of a transistor is formed of a transparent film. Forinstance, Japanese Patent Application Laid-Open No. 2002-76356 disclosesa TFT (thin film transistor) which employs a polycrystalline thin filmof a transparent conductive oxide containing ZnO as a main component,for a channel layer.

In addition, an organic electroluminescent light-emitting device hasbeen actively researched and developed. When the organicelectroluminescence is applied to a display unit, it is driven in anactive matrix fashion in most cases. For the active matrix drive, a TFTwhich uses amorphous silicon or polysilicon is generally utilized.

In addition, Japanese Patent Application Laid-Open No. H09-114398discloses an organic electroluminescent display unit which preventsdegradation of a driving device, can display a television image, andaims at realizing a high-quality/high-luminance display unit. Theorganic electroluminescent display unit of an active matrix typeaccording to this patent document is intended to prevent degradation ofthe driving device while keeping the high image quality, by using twoMOS (metal oxide semiconductor) field effect transistors which usesingle-crystal silicon for an active layer.

In addition, Japanese Patent Application Laid-Open Nos. 2006-165528 and2006-186319 disclose an example of producing a field effect transistorby using an amorphous oxide which is prepared by adding a specifiedamount of gallium or the like to a zinc-indium-based oxide to controlthe electron carrier concentration to less than 10¹⁸/cm³, and ofapplying the field effect transistor to an image display apparatus or alight-emitting apparatus.

In the conventional organic light-emitting/display apparatus, sinceamorphous silicon or polysilicon is used mainly as an active layer(channel layer) of a driving transistor, the gate insulating layer andthe interlayer insulating layer can be used with no distinction.Further, since amorphous silicon or polysilicon used for the activelayer originally contains hydrogen atoms, the diffusion of hydrogen inthe insulating layers has posed no problem in most cases. Hydrogen in ana-SiN:H film produced by a plasma CVD (chemical vapor deposition)process has been rather considered to have an effect of compensatingdefects in amorphous silicon.

On the other hand, there has been found such a phenomenon that when anoxide semiconductor is used as an active layer of a driving transistor,there are a case where the transistor performs driving without anyparticular problem and a case where the off-state current increasesduring driving for a long period of time for unknown reasons. Thephenomenon seems to depend on a method of forming an insulating layerwhich is in contact with an oxide semiconductor active layer, but thereason has not been clarified. Accordingly, there has been a problemthat degradation of the characteristics may sometimes be caused due tothe phenomenon. Moreover, the degradation of the characteristics hasbeen intensively occurred during active matrix driving for a long periodof time.

As described above, the conventional oxide semiconductor has the problemthat when used in a stacked device, if a large amount of hydrogen iscontained in an insulating layer, the degradation of the characteristicsis liable to be occurred due to diffusion of the hydrogen. The problemhas remarkably appeared in a display apparatus which employs the oxidesemiconductor particularly for an active layer of a TFT. In this case,there has been a problem that a display apparatus cannot be realizedwhich is stably driven for a long period of time and displays an imagewith high definition and less image defect.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished to dissolve the abovedescribed problems, and provides a display apparatus which can be stablydriven for a long period of time without degrading the high mobility andhigh characteristics peculiar to an oxide semiconductor, and can displayan image with high definition and less image defect, and a productionmethod of the display apparatus.

In order to achieve the above-mentioned object, according to one aspectof the present invention, there is provided a display apparatus whichincludes a light-emitting layer, a pair of electrodes sandwiching thelight-emitting layer, a transistor with an active layer for driving thelight-emitting layer through the pair of the electrodes, and a matrixwiring portion having a scanning electrode line, a signal electrodeline, and a first insulating layer, wherein the active layer includes anoxide which contains In and Zn and at least a part of which isamorphous, and wherein a second insulating layer containing hydrogen inan amount of less than 3×10²¹ atoms/cm³ is disposed between the activelayer and the first insulating layer.

Further, according to another aspect of the present invention, there isprovided a method of producing a display apparatus, which includesforming a matrix wiring portion having a scanning electrode line, afirst insulating layer and a signal electrode line; forming a transistorwith an active layer including an oxide which contains In and Zn and atleast a part of which is amorphous; forming a second insulating layercontaining hydrogen in an amount of less than 3×10²¹ atoms/cm³ betweenthe first insulating layer and the active layer; and forming alight-emitting layer and a pair of electrodes sandwiching thelight-emitting layer.

According to the present invention, a display apparatus is providedwhich can display an image with high definition and less image defect,because a transistor with an active layer which includes an oxidecontaining In and Zn and at least a part of which is amorphous canstably perform driving for a long period of time. Thereby, the presentinvention can provide a bottom-emission type display apparatus, atop-emission type display apparatus or a two-sided emission typehigh-luminance display apparatus which maintains superior stability fora long period of time.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical representation illustrating a relationship betweenthe amount of hydrogen ions injected into an In—Ga—Zn—O-based amorphousfilm and the electrical resistance of the film.

FIG. 2 is a graphical representation illustrating a distributed state ofhydrogen atoms contained in an insulating layer, which have diffusedinto an In—Ga—Zn—O-based amorphous film.

FIG. 3 is a graphical representation illustrating a concentration ofhydrogen atoms in an insulating layer according to the presentinvention.

FIG. 4 is a graphical representation illustrating Id-Vg characteristicsof a TFT using a gate insulating layer containing a large amount ofhydrogen.

FIG. 5 is a graphical representation illustrating Id-Vg characteristicsof a TFT using a gate insulating layer containing a small amount ofhydrogen according to the present invention.

FIG. 6 is a graphical representation illustrating a relationship betweena concentration of hydrogen atoms in a gate insulating layer accordingto the present invention and an ON/OFF ratio in TFT characteristics.

FIG. 7A is a plan view of a representative pixel portion used in adisplay apparatus according to an embodiment of the present invention;FIG. 7B is a cross-sectional view taken along line 7B-7B in FIG. 7A; andFIG. 7C is a cross-sectional view taken along line 7C-7C in FIG. 7A.

FIG. 8 is a circuit diagram of a display apparatus having a plurality ofmatrix lines according to an embodiment of the present invention.

FIG. 9A is a plan view of a representative pixel portion used in adisplay apparatus according to an embodiment of the present invention;and FIG. 9B is a cross-sectional view taken along line 9B-9B in FIG. 9A.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of a display apparatus according to the present inventionwill now be specifically described below with reference to the drawings.

At first, a summary of the present invention will now be described.

The present inventors have energetically carried out a research on anoxide semiconductor active layer, a gate insulating layer, and aninterlayer insulating layer of a TFT, and film growth conditions relatedthereto. As a result, the present inventors have found that a TFTexcellent in long-term stability can be obtained by controlling acondition of an oxygen atmosphere during film formation, and controllingthe content of hydrogen in the gate insulating layer and the interlayerinsulating layer, and then accomplished the present invention.

The present inventors have found that a normally-off type TFT withexcellent mobility can be made from an oxide semiconductor active layerhaving a desired electron carrier concentration and a Y₂O₃ insulatinglayer and can be applied to a light-emitting apparatus, an image displayapparatus or the like. Thereafter, it has been confirmed that fewelements do not normally operate when subjected to a repetitive lightemission test of a long period of time and that in particular, a devicewith a matrix wiring often shows such tendency.

Further thereafter, the present inventors have found that when aninterlayer insulating layer in a matrix wiring portion is a-SiNx:Hformed by low temperature plasma CVD, the change in stability isremarkable, and have further made extensive study. As a result, thepresent inventors have found that by forming an insulating layer havinga hydrogen content of less than 3×10²¹ atoms/cm³ by using sputtering andthen forming an oxide semiconductor active layer of a TFT on theinsulating layer, there is obtained an effect of remarkably improvingthe long-term stability of the TFT. A similar effect can also beobtained by an embodiment in which a portion other than a portion beingin a contact with a source electrode and a drain electrode of an oxidesemiconductor active layer of a TFT is covered with an insulating layerhaving the same hydrogen content as described above.

Here, the insulating layer in contact with the oxide semiconductoractive layer was formed by controlling the hydrogen content to be lessthan 3×10²¹ atoms/cm³. The insulating layer can be formed by using asputtering process, but the forming method in the present invention isnot limited to sputtering. For instance, the hydrogen content can alsobe controlled to be less than 3×10²¹ atoms/cm³ by forming an amorphoussilicon nitride (a-SiNx:H) film by using a low-temperature plasma CVDprocess and heating the film to 450° C. by using a rapid thermalannealing process. Further, the insulating layer can be made by using ahigh-temperature plasma CVD process as well.

The present invention has been accomplished based on such findings, andprovides a display apparatus using the above described film. Embodimentsof the display apparatus according to the present invention will now bedescribed in detail below.

The display apparatus according to the present embodiment includes (1)TFTs; (2) a light-emitting layer; (3) lower and upper electrodes (a pairof electrodes) which sandwich the light-emitting layer; and (4) a matrixwiring portion having a scanning electrode line, a first insulatinglayer, and a signal electrode line. In this configuration, an activelayer of the TFT includes an oxide which contains In and Zn and at leasta part of which is amorphous, and a second insulating layer containinghydrogen in an amount of less than 3×10²¹ atoms/cm³ is disposed betweenthe active layer and the first insulating layer.

In this configuration, the hydrogen content in the second insulatinglayer is preferably less than that in the first insulating layer. Inaddition, of the active layer of the TFT, a portion of the active layerother than a portion being in contact with a source electrode and adrain electrode may be covered with the second insulating layer havingthe above-mentioned hydrogen content of less than 3×10²¹ atoms/cm³.Furthermore, the first insulating layer may have a hydrogen content ofless than 3×10²¹ atoms/cm³. In addition, the TFTs may be disposed inseries on the top of the matrix wiring portion composed of the scanningelectrode line, the first insulating layer, and the signal electrode, ordisposed in parallel on a part adjacent thereto. Furthermore, the TFTsmay be disposed on the top of the matrix wiring portion composed of thescanning electrode line, the first insulating layer, and the signalelectrode or on a part adjacent thereto with the second insulating layerformed by a sputtering step being used as a gate insulating layer. Thefirst insulating layer corresponds to the interlayer insulating layer ofthe matrix wiring portion. The second insulating layer mainlycorresponds to a gate insulating layer of the TFT, but is not limitedthereto, and may be constituted by an insulating layer wholly covering aportion other than a portion being in contact with a source electrodeand a drain electrode of the TFT.

A method of producing a display apparatus according to the presentembodiment includes: (1) forming a matrix wiring portion; (2) forming aTFT; (3) forming a second insulating layer; (4) forming a light-emittinglayer; and (5) forming a pair of electrodes (lower and upper electrodes)which sandwich the light-emitting layer. The matrix wiring portion has ascanning electrode line, an interlayer insulating layer (a firstinsulating layer), and a signal electrode line. The TFT has an activelayer including an oxide which contains In and Zn and at least a part ofwhich is amorphous. The second insulating layer has a hydrogen contentof 3×10²¹ atoms/cm³. The pair of the electrodes are the upper and lowerelectrodes which sandwich the light-emitting layer.

For the display apparatus according to the present embodiment, thefollowing production methods can be adopted.

1) First, a matrix wiring portion is formed which is composed of ascanning electrode line, an interlayer insulating layer, and a signalelectrode line. Subsequently, a TFT is formed thereon which has anactive layer and a second insulating layer formed by a sputtering step.Then, a lower electrode, a light-emitting layer, and an upper electrodeare formed.

2) First, a matrix wiring portion composed of a scanning electrode line,a first insulating layer, and a signal electrode line, and a lowerelectrode are formed. Subsequently, a TFT having an active layer and asecond insulating layer formed by a sputtering step, a light-emittinglayer, and an upper electrode are formed.

3) First, a matrix wiring portion is formed which is composed of ascanning electrode line, a first insulating layer, and a signalelectrode line. Subsequently, a TFT having a portion of an active layerother than a source electrode and a drain electrode covered with asecond insulating layer formed by a sputtering step, a light-emittinglayer, a lower electrode, and an upper electrode are formed.

4) First, a matrix wiring portion composed of a scanning electrode line,a first insulating layer, and a signal electrode line, and a lowerelectrode are formed. Subsequently, a TFT having a portion of an activelayer other than a source electrode and a drain electrode covered with asecond insulating layer formed by a sputtering step, a light-emittinglayer, and an upper electrode are formed.

A display apparatus according to the present embodiment will now bedescribed below in detail with particular focus on an oxidesemiconductor active layer and the second insulating layer having thehydrogen content of less than 3×10²¹ atoms/cm³.

(Transparent Amorphous Oxide Film)

First, as an oxide semiconductor active layer, a transparent amorphousoxide film containing electron carriers in a concentration of less than10¹⁸/cm³ according to the present inventors will be described.

The above-mentioned transparent amorphous oxide film is specificallyconstituted by including In—Ga—Zn—O and has a composition represented byInGaO₃(ZnO)_(m), wherein m is a natural number of less than 6, in acrystal state, and has an electron carrier concentration of less than10¹⁸/cm³. It is also preferred to control the electron mobility in thisfilm to be 1 cm²/(V·sec) or more.

When the above-mentioned film is used in a channel layer (active layer)of a TFT, a TFT can be produced which is of a normally off type in whichthe gate current is less than 0.1 μA when the transistor is in an offstate, has transistor characteristics of an ON/OFF ratio exceeding 10³,and is transparent to visible light and flexible. In addition, theelectron mobility of the above-mentioned transparent amorphous oxidefilm increases with increase of the number of conduction electrons. As asubstrate for formation of the transparent amorphous oxide film, theremay be used a metal substrate, a metal thin plate, a glass substrate, aplastic substrate, or a plastic film.

The present inventors have found that such a transparent amorphous oxidefilm has specific characteristics in which the electron mobilityincreases as the number of conduction electrons increases. Further, theyhave also found that a TFT formed by using the film has further improvedtransistor characteristics such as an ON/OFF ratio, a saturation currentin a pinched-off state and a switching speed.

When using the transparent amorphous oxide film for a channel layer of athin film transistor, it is preferable to control the electron mobilityto be 1 cm²/(V·sec) or more and also to control the electron carrierconcentration to be less than 10¹⁸/cm³. It is further preferable tocontrol the electron mobility to be 5 cm²/(V·sec) or more and to controlthe electron carrier concentration to be less than 10¹⁶/cm³. Byrespectively controlling the electron mobility and the electron carrierconcentration within the above-mentioned ranges, the electric currentflowing between the drain and source terminals in an off-state (when agate voltage is not applied) can be made less than 10 μA, preferablyless than 0.1 μA.

By using the thin film, when the electron mobility is 1 cm²/(V·sec) ormore and preferably 5 cm²/(V·sec) or more, the saturation current afterpinch-off can be made more than 10 μA. Further, the ON/OFF ratio can bemade 10³ or more. In the TFT in a pinched-off state, a high voltage isapplied to the gate terminal, and electrons exist in the channel at ahigh density.

Thus, according to the present invention, the saturation current valuecan be increased by an amount corresponding to the increase of theelectron mobility. As a result, almost all the transistorcharacteristics are improved including ON/OFF ratio increase, saturationcurrent increase, and switching speed increase. Incidentally, in anormal compound, when the number of electrons increases, the electronmobility decreases because electrons collide with each other.

As the structure of the above described TFT, a staggered (top gate)structure can be adopted in which a gate insulating film and a gateterminal are sequentially formed on a semiconductor channel layer.Furthermore, an inverted staggered (bottom gate) structure can also beadopted in which a gate insulating film and a semiconductor channellayer are sequentially formed on a gate terminal.

(Film Composition)

In a transparent amorphous oxide thin film having a compositionrepresented by InGaO₃(ZnO)_(m) (wherein m is a natural number of lessthan 6) in a crystal state, when the value of m is less than 6, theamorphous state is stably kept up to a high temperature of 800° C. ormore. However, as the value of m increases, the ratio of ZnO to InGaO₃increases, i.e., the composition approaches to a ZnO composition, thefilm becomes liable to be crystallized. Accordingly, when the film isused for a channel layer of an amorphous TFT, the value of m ispreferably less than 6.

(Implantation of Hydrogen Ions into Transparent Amorphous Oxide Film)

An amorphous oxide of In—Ga—Zn was prepared by using a sputterevaporation process while using a polycrystal sintered body having acomposition of InGaO₃(ZnO)_(m) (wherein m is a natural number of lessthan 6) as a target and also using argon gas and oxygen gas as anatmospheric gas. The film formation was performed while controlling thesubstrate temperature to room temperature, setting the sputteringpressure to 0.48 Pa and setting the oxygen gas ratio to 5%. Hydrogenions were implanted into the resulting deposited film of the transparentamorphous oxide (a-InGaZn:O), and the change of resistivity (Ωm)depending on the implantation amount (1/cm³) of hydrogen ions wasobserved. The result is shown in FIG. 1.

It can be seen from the result shown in FIG. 1 that the resistivity ofthe transparent amorphous oxide film changes by 4 to 5 digits in thevicinity of a hydrogen ion implantation amount of 10¹⁹/cm², and theresistance of the film decreases as the hydrogen ion implantation amountincreases. This reveals the effect of hydrogen ions implanted into thetransparent amorphous oxide (a-InGaZn:O) film. However, the value ofhydrogen ion implantation amount of 10¹⁹/cm³ is not a fixed value, andthe hydrogen ion implantation amount at which the resistivity changeswill vary depending on the preparation conditions or method.

(Hydrogen Atom Concentration in Insulating Layer)

The concentrations of hydrogen atoms contained in a-SiN:H, a-SiN_(x),a-SiO_(x):H, and a-SiO_(x) prepared by a plasma-CVD process or asputtering process was measured with an SIMS (Secondary Ion MassSpectrometry) measurement equipment. The result is shown in FIG. 2. Itcan be seen from the result shown in FIG. 2 that the concentration ofhydrogen atoms in an a-SiN:H film produced by a plasma-CVD process is1×10²² atoms/cm³, and that hydrogen atoms diffuse from inside of thea-SiN:H film into an a-InGaZn:O film.

Similarly, the concentration of hydrogen atoms in the insulating layerproduced by a sputtering step was measured. The result is shown in FIG.3. It can be seen from the result that the concentration of hydrogenatoms in the insulating layer (a-SiO_(x)) prepared by the sputteringprocess is less than 3×10²¹ atoms/cm³.

It has been confirmed from the measurement result that the concentrationof hydrogen atoms in an insulating layer can be reduced by thepreparation conditions or method.

(Dependency of TFT Characteristics on Amount of Hydrogen Atoms in GateInsulating Layer)

The change over time of a TFT including a gate insulating layercontaining a large amount of hydrogen atoms (hydrogen atomconcentration: 1×10²² atoms/cm³) was compared in terms of Id-Vgcharacteristics. The result is shown in FIG. 4. It can be seen from theresult that the off-state current increases with the elapse of time andfinally a state in which the TFT cannot turn on/off is reached.

On the other hand, FIG. 5 shows a change over time of a TFT using a gateinsulating layer containing a small amount of hydrogen atoms (hydrogencontent: less than 3×10²¹ atoms/cm³). In this case, little change wasobserved, and good characteristics were maintained.

In addition, FIG. 6 shows a relationship between the concentration ofhydrogen atoms in the gate insulating layer and an ON/OFF ratio of TFTcharacteristics at the time of 20 days after the preparation. Theresults mean that the TFT shows better characteristics when containingthe hydrogen atom concentration to at least less than 3×10²¹ atoms/cm³.This is considered to be because the resistance of the oxidesemiconductor decreased due to the diffusion of hydrogen into the oxidesemiconductor layer and a high ON/OFF ratio was not able to be attained,as is seen from the above described results.

As described above, SiO_(x) or SiN_(x) is preferable for the gateinsulating layer to be used in a thin film transistor using atransparent amorphous oxide film. However, it can be seen that in orderto maintain the stability for a long period of time, it is indispensableto set the hydrogen content in the insulating layer to be less than3×10²¹ atoms/cm³, and that in the case of a film having a large hydrogencontent, the characteristics change with the elapse of time and theoff-state current increases. Moreover, it is easily assumed that thesame also applies to the contents of hydrogen in other insulating layerssuch as of Al₂O₃, Y₂O₃, or HfO₂ film. According to the findings of thepresent inventors, the effect of the present invention is obtained aslong as the hydrogen content in the insulating layer is less than 3×10²¹atoms/cm³, so that there is no lower limit in the hydrogen content inparticular. Accordingly, the lower limit of the hydrogen content in theinsulating layer is ideally zero.

In addition, when there is a defect in an interface between a gateinsulating thin film and a channel layer thin film, the electronmobility decreases and a hysteresis is generated in the transistorcharacteristics.

In addition, a leak current greatly differs depending on the type of agate insulating film. Accordingly, a gate insulating film needs to beselected so as to match a channel layer.

In addition, the gate insulating film and the channel layer can beformed at room temperature, so that any TFT structure of a staggeredstructure and an inverted staggered structure can be formed.

The TFT is a three-terminal device having a gate terminal, a sourceterminal, and a drain terminal, and employs a semiconductor thin filmformed on an insulation substrate such as of ceramic, glass or plasticas a channel layer through which electrons or holes move. Moreover, theTFT is also an active device which has a function of, in operation,applying a voltage to the gate terminal to control an electric currentflowing in the channel layer, thereby switching an electric currentbetween the source terminal and the drain terminal.

In the next place, a display apparatus according to an embodiment of thepresent invention will be specifically described.

The present embodiment relates to a display apparatus using the abovedescribed transparent amorphous oxide film. Specifically, the embodimentrelates to a display apparatus driven by TFTs each using a semiconductorwhich is the above described transparent amorphous oxide film, and inparticular, relates to a light source and a display unit for emittinglight by driving an organic EL device. Thereby, the present embodimentcan provide a display apparatus using a substrate even made of a plasticor the like which is lightweight and is hardly cracked.

In the next place, a basic configuration of a display apparatusaccording to the present embodiment will be described with reference toFIGS. 7A, 7B and 7C.

In the figures, reference numeral 400 denotes a substrate, referencenumeral 401 denotes a power supply line, reference numeral 402 denotes aGND (grounding) line, reference numeral 403 denotes a signal electrodeline, reference numeral 404 denotes a first insulating layer (interlayerinsulating layer), and reference numeral 405 denotes a contact electrodeembedded in each contact hole. In addition, reference numeral 406denotes a gate electrode, reference numeral 407 denotes a scanningelectrode line, reference numeral 408 denotes a second insulating layer,reference numeral 409 denotes an amorphous oxide semiconductor,reference numeral 410 denotes a source electrode and a drain electrode,reference numeral 411 denotes a lower electrode, reference numeral 412denotes a third insulating layer, reference numeral 413 denotes alight-emitting layer, and reference numeral 414 denotes an upperelectrode. Among them, the second insulating layer 408 and the thirdinsulating layer 412 together constitute the second insulating layeraccording to the present invention.

At first, the power supply line 401, the GND line 402, and the signalelectrode line 403 are patterned on the substrate 400, and subsequentlythe first insulating layer 404 is deposited, contact holes are formed atdesired positions of the first insulating layer 404, and the contactelectrodes 405 are further embedded at the desired positions.

Next, the gate electrode 406 and the scanning electrode line 407 arepatterned on the first insulating layer 404. At this time, the gateelectrodes 406 are disposed in desired positions according to thenecessary number of transistors, and electrodes (not shown) for thenecessary number of capacitors are also patterned. Thus, it is one ofthe key features of the present invention to form a matrix wiringportion before forming a transistor.

Subsequently, the second insulating layer 408 having a hydrogen contentof less than 3×10²¹ atoms/cm³ is formed by a sputtering step.Furthermore, contact holes are formed at desired positions of the secondinsulating layer 408, and contact electrodes are embedded in the contactholes.

Next, the lower electrode 411 of the light-emitting portion is formed soas to be connected to the power supply line 401 through the contactelectrode 405, and an amorphous oxide semiconductor 409 is patterned onthe second insulating layer 408. Subsequently, a source electrode and adrain electrode 410 are formed, and one of the electrodes is connectedto a GND line 402 through the contact electrode.

Next, in order to protect the channel portion of the transistor, thethird insulating layer 412 having a hydrogen content of less than 3×10²¹atoms/cm³ is formed by a sputtering step. Subsequently, a light-emittinglayer 413 composed of a hole-transporting layer, a light-emittingportion and an electron-transporting layer (not shown) is formed on thelower electrode 411. Subsequently, the upper electrode 414 is depositedon the light-emitting layer 413, and the upper electrode 414 isconnected to the other electrode of the source electrode and the drainelectrode 410.

The light-emitting layer 413 is not limited to the above describedconfiguration. Further, when the TFT is in an ON state, a voltage isapplied to the light-emitting layer 413 to emit light. As the upperelectrode 414, a metal electrode is used when the light-emitting deviceis used as a bottom emission type device, and a transparent electrodemay be used when the light-emitting device is used as a two-sidedemission type device. The material can be changed according to theintended use of the light-emitting device.

In the next place, each component of a display apparatus used in thepresent embodiment will be described in detail.

1. Substrate

A glass substrate is generally used in a image display apparatus.However, in principle, a substrate to be used in the present inventionis not particularly limited as long as it has flatness. Since the TFTused in the present invention can be formed at a low temperature, aplastic substrate, which is generally hard to be used for an activematrix type display apparatus, can be used. Thereby, an image displayapparatus is obtained which is lightweight and is hardly broken. Theimage display apparatus can be bent to a certain extent.

In addition to the glass substrate and the plastic substrate, asemiconductor substrate such as of Si or a ceramic substrate can also beused. In addition, a substrate having an insulating layer provided on ametal substrate can be used as long as it is flat.

2. Transistor

As the active layer, an In—Ga—Zn—O-based semiconductor is used. For thiscomposition, substitution with or addition of an element such as Mg canbe performed as long as the semiconductor has desired characteristics,that is, the electron carrier concentration is less than 10¹⁸/cm³ andthe electron mobility is more than 1 cm²/(V·sec).

As described above, a sputtering process or a pulsed laser evaporationprocess is suitable for forming the active layer, but various sputteringprocesses which are advantageous in productivity are more preferable. Inaddition, it is effective to appropriately insert a buffer layer betweenthe active layer and a substrate.

For the gate insulating film, there are preferably used Al₂O₃, Y₂O₃,HfO₂, SiO_(x), and SiN_(x) as described above. However, in order tomaintain the long-term stability, it is indispensable that the hydrogencontent in the insulating layer is less than 3×10²¹ atoms/cm³.

3. Lower Electrode

When the light-emitting layer is of a current injection type representedby an organic electroluminescent device, a preferred electrode isadopted according to the configuration thereof. For instance, when thelower electrode is connected as an anode to the light-emitting layer,the lower electrode is preferably a transparent electrode having a largework function. Examples of such material include ITO, electroconductiveZnO or In—Zn—O having an electron carrier concentration of 10¹⁸/cm³ ormore. Alternatively, In—Ga—Zn—O-based oxide having an electron carrierconcentration of 10¹⁸/cm³ or more can be used as well. In this case, incontrast to the case of a TFT, a larger carrier concentration, forinstance, 10¹⁹/cm³ or more is more preferable.

4. Light-Emitting Layer

The light-emitting layer is not particularly limited as long as it canbe driven by an In—Ga—Zn—O-based TFT, but is preferably an organicelectroluminescent layer in particular.

The light-emitting layer used in the present invention is generallycomposed of a plurality of layers such as

(1) hole-transporting layer/(light-emittingportion+electron-transporting layer) (meaning a light-emitting portionhaving an electron-transporting function);(2) hole-transporting layer/light-emitting portion/electron-transportinglayer;(3) hole injection layer/hole-transporting layer/light-emittingportion/electron-transporting layer;(4) hole injection layer/hole-transporting layer/light-emittingportion/electron-transporting layer/electron injection layer.

In addition, there are cases where an electron barrier layer or anadhesion improving layer is additionally provided. Among the aboveexamples, a representative light-emitting layer is composed ofhole-transporting layer/light-emitting section/electron-transportinglayer. Incidentally, the light-emitting layer according to the presentinvention is not limited to these configurations.

For the light-emitting layer, fluorescence and phosphorescence areutilized, but it is effective to utilize the phosphorescence from theviewpoint of emission efficiency. As the phosphorescent material, aniridium complex is useful. Further, as the compound used, both a lowmolecular compound and a high molecular compound are available. Ingeneral, the low molecular compound can be formed into a film by vapordeposition, and the high molecular compound can be formed into a film byink jet or printing. Examples of the low molecular compound include anamine complex, an anthracene, a rare earth complex, and a noble metalcomplex. Examples of the high molecular compound include π-conjugated orpigment-containing polymers.

As the material of the electron injection layer, there are included analkali metal, an alkaline earth metal and a compound thereof; and anorganic layer doped with an alkali metal.

Further, as the material of the electron-transporting layer, there areincluded an aluminium complex, oxadiazole, triazole, and phenanthroline.

Moreover, as the material of the hole injection layer includes anarylamine, a phthalocyanine, and an organic layer doped with a Lewisacid.

Furthermore, as the material of the hole-transporting layer, anarylamine is included.

5. Upper Electrode

The preferred material of the upper electrode varies depending onwhether the light emitting device is used as a two-sided emission typeor a bottom emission type, and whether the upper electrode is used ananode or a cathode.

When used as the two-sided emission type, the upper electrode needs tobe transparent. Examples of the material of the transparent electrodeincludes oxides such as electroconductive ZnO, In—Zn—O, or ITO, whichcontains at least one element of In and Zn, is formed under depositionconditions including an oxygen flow rate adjusted such that the electroncarrier concentration is 10¹⁸/cm³ or more, and at least a part of whichis amorphous. Alternatively, an In—Ga—Zn—O-based oxide having anelectron carrier concentration of 10¹⁸/cm³ or more can be used.Moreover, the upper electrode can be prepared by forming an alloy dopedwith an alkali metal or an alkaline earth metal into a film of several10 nm or less in thickness and forming a transparent electrode thereon.

In the case of the bottom emission type, the upper electrode does notneed to be transparent. Accordingly, when the upper electrode is used asthe anode, the usable material includes an Au alloy or a Pt alloy havinga large work function, and when used as the cathode, the usable materialincludes Ag-added Mg, Li-added Al, a silicide, a boride, and a nitride.

In the present embodiment, a matrix wiring portion is formed beforehand(in which an interlayer insulating film used is normally a-SiOx:H,a-SiNx:H, a-SiNOx:H or the like produced by a PCVD (Plasma ChemicalVapor Deposition) process). Subsequently, an insulating layer isseparately formed by using a method which is difficult to incorporatehydrogen into the insulating layer, and then an oxide semiconductorlayer is formed and a pixel circuit is produced. As described above, thedisplay apparatus according to the present embodiment uses a TFT formedof or protected by the insulating layer having the small hydrogencontent, and therefore can solve the problem that in the case where aconventional oxide semiconductor is used for a stacked device, when aninsulating layer contains much hydrogen, the characteristics of thedevice are liable to be degraded due to the diffusion of the hydrogen.Thereby, the present invention can provide a display apparatus whichdoes not degrade the high mobility and excellent characteristicspeculiar to the oxide semiconductor and is stably operated.

Application Example

A configuration example in which the above described embodiment isapplied to a display apparatus having a plurality of matrix wirings willnow be described with reference to FIG. 8.

In the figure, reference numeral 55 denotes a selecting transistor whichselects a pixel, and reference numeral 56 denotes a driving transistorwhich drives a light-emitting layer 58. In addition, a capacitor 57 isprovided for keeping a selected state, stores an electric charge betweena GND line 53 and a source electrode of the selecting transistor 55, andholds a signal of a gate of the driving transistor 56. The pixel isselected by a scanning electrode line 51 and a signal electrode line 52.

Specifically, the operation will now be described. An image signal froma driver circuit (not shown) is applied to a gate electrode in a form ofa pulse signal through the scanning electrode line 51. At the same time,another pulse signal from another driver circuit (not shown) is appliedto the selecting transistor 55 through the signal electrode line 52,whereby a pixel is selected. At that time, the selecting transistor 55is turned on, and an electric charge is stored in the capacitor 57provided between the GND line 53 and the source of the selectingtransistor 55. Thereby, a gate voltage of the driving transistor 56 iskept at a desired voltage, and the driving transistor 56 is turned on.This state is maintained until a next signal is received. While thedriving transistor 56 is in the ON state, a voltage and an electriccurrent continue to be supplied to the light-emitting layer 58 tocontinue light emission.

The example illustrated in FIG. 8 has the configuration in which onepixel has two transistors and one capacitor, but one pixel may have alarger number of transistors integrated therein in order to improve theperformance. It is sufficient that an amorphous oxide semiconductorcontaining at least In and Zn is used in the portion of an active layerof a transistor and an insulating layer having a hydrogen content ofless than 3×10²¹ atoms/cm³. Further, it is preferred that a matrixwiring portion such as a scanning electrode line, a signal electrodeline, and a power supply line is formed prior to the formation of thetransistor portion. Thereby, an image display apparatus can be obtainedwhich is excellent in long-term repetition characteristics.

Another Embodiment

In the next place, a basic configuration of a display apparatusaccording to another embodiment of the present invention will bedescribed with reference to FIGS. 9A and 9B.

In the figure, reference numeral 600 denotes a substrate, referencenumeral 601 denotes a lower electrode, reference numeral 602 denotes apower supply line, reference numeral 603 denotes a signal electrodeline, reference numeral 604 denotes a GND line, and reference numeral605 denotes a first insulating layer (interlayer insulating layer). Inaddition, reference numeral 606 denotes a gate electrode, referencenumeral 607 denotes a second insulating layer, reference numeral 608denotes an amorphous oxide semiconductor, reference numeral 609 denotesa source electrode and a drain electrode, reference numeral 610 denotesa third insulating layer, reference numeral 611 denotes a bank,reference numeral 612 denotes a light-emitting layer, and referencenumeral 613 denotes an upper electrode. Among the above-mentionedelements, the second insulating layer 607 and the third insulating layer610 together constitute the second insulating layer according to thepresent invention.

In the figure, at first, the lower electrode 601 of the light-emittinglayer 612 is patterned on the substrate 600. Furthermore, after a metallayer is deposited, the power supply line 602, the signal electrode line603, and the GND line 604 are also patterned. At this time, the powersupply line 602 is patterned so as to be in contact with the lowerelectrode 601.

Subsequently, after the first insulating layer 605 is deposited andpatterned, contact holes are formed at desired positions of the firstinsulating layer 605, and then contact electrodes are embedded in thecontact holes. Subsequently, the gate electrode 606 and a scanningelectrode line (not shown) are patterned at desired positions on thefirst insulating layer 605. At this time, the gate electrodes 606 aredisposed corresponding to the necessary number of transistors, andelectrodes (not shown) for the necessary number of capacitors are alsopatterned. As described above, it is also one of the key features of thepresent invention that the matrix wiring portion is formed before theformation of the transistor.

Next, the second insulating layer 607 having a hydrogen content of lessthan 3×10²¹ atoms/cm³ is formed thereon. Furthermore, a contact hole isformed at a desired position of the second insulating layer 607, and acontact electrode is embedded in the contact hole. In addition, anamorphous oxide semiconductor 608 which becomes an active layer of thetransistor is patterned on the second insulating layer 607.Subsequently, the source electrode and drain electrode 609 are formed,and one of the electrodes is connected to the GND line 604 through thecontact electrode. Next, the third insulating layer 610 having ahydrogen content of less than 3×10²¹ atoms/cm³ is formed thereon with asputtering step so as to protect the channel portion of the transistor.Subsequently, on the lower electrode 601, the light-emitting layer 612is formed which is composed of a hole-transporting layer, alight-emitting portion, an electron-transporting layer and the like (notshown). Subsequently, the upper electrode 613 is deposited, and the thusformed upper electrode 613 is connected to the other of the sourceelectrode and drain electrode 609.

Incidentally, the light-emitting layer 612 is not limited to the abovedescribed configuration. Further, when the TFT is in an ON state, avoltage is applied to the light-emitting layer 612 to emit light. As theupper electrode 613, a metal electrode is used when the light-emittingdevice is used as a bottom emission type device, and a transparentelectrode may be used when the light-emitting device is used as atwo-sided emission type device. The material can be changed according tothe intended use of the light-emitting device.

A display apparatus according to the present invention and a productionmethod thereof will now be described in detail below.

Example 1

In the first place, Example 1 according to the present invention willnow be described.

At first, a SiO₂ glass substrate (1737 manufactured by Corning, Inc.)was prepared as a substrate for film formation. As the pretreatmentbefore film formation, the substrate was ultrasonically degreased andcleaned with acetone, IPA (isopropanol), and ultrapure watersequentially for five minutes each and then dried at 100° C. in air.

Subsequently, a film with a thickness of 200 nm was deposited by a DC(direct current) sputtering process using Al—Si (5%) as a targetmaterial, and then a power supply line, a GND line, and a signalelectrode line were patterned at desired positions by using aphotolithographic process and a dry process.

Next, a film of a-SiNx:H was deposited thereon as an interlayerinsulating layer in a thickness of 600 nm at a substrate temperature of300° C. using a plasma-CVD process. Subsequently, contact holes wereformed in desired positions, and electrodes were embedded so as tocontact the power supply line, the GND line, and the signal electrodeline. Furthermore, films of Ti/Au/Ti were deposited in thicknesses of 5nm/40 nm/5 nm respectively with a DC sputtering process using Au and Tias target materials. Thereafter, a scanning electrode line, two gateelectrodes for TFT and an electrode for a capacitor were formed atdesired positions with a photolithographic process and a lift-offprocess.

Thus, a matrix wiring portion was formed on the substrate, and then thegate electrode for the TFT and the electrode for the capacitor wereformed thereon.

Next, a second insulating layer having a hydrogen content of less than3×10²¹ atoms/cm³ was formed on the substrate having the matrix wiringportion formed thereon. A sintered body (with a size of 98 mm indiameter and 5 mm in thickness) having a composition of SiO₂ was usedfor the target material. A deposition chamber was controlled to reach avacuum degree of 2.0×10⁻⁴ Pa. In the deposition chamber, Ar gas wasflown at 133 Pa for 20 minutes before the film formation, andpre-sputtering was performed for five minutes. During the filmformation, the total pressure in the chamber was controlled to aconstant value of 0.1 Pa, Ar gas was flown at 10 sccm, and the distancebetween the target and the film-forming substrate was set at 75 mm. Theinput power was RF 400 W, and the film forming rate was 7 nm/min. Thedeposited film thickness of the second insulating layer was 200 nm.Furthermore, contact holes were formed in the second insulating layerwith a dry etching process. The dry etching was performed under theconditions of CF₄ gas 20 sccm, 5 Pa, and RF 150 W at an etch rate of 41nm/min for 5.5 minutes.

Next, an amorphous oxide semiconductor was formed as the active layer ofthe TFT. A polycrystal sintered body (with a size of 98 mm in diameterand 5 mm in thickness) having the composition of InGaO₃(ZnO)₄ was usedfor the target material. The sintered body was prepared by dry mixingIn₂O₃, Ga₂O₃ and ZnO (each 4N reagent) as starting materials (solvent:ethanol), followed by presintering (1,000° C.; 2 hours), dry milling,and sintering (1,500° C.; 2 hours). The target had an electricalconductivity of 12 S/cm and was in a semi-insulating state. The vacuumreached in the deposition chamber was 3.0×10⁻⁴ Pa. During the filmformation, the total pressure in the deposition chamber was controlledto a constant value of 0.5 Pa, and the oxygen gas ratio was controlledto 5%. In addition, the distance between the target and the film-formingsubstrate was set at 75 mm. The input power was RF 200 W, and thefilm-forming rate was set at 7.1 nm/min. The deposited film thickness ofthe amorphous oxide semiconductor was 40 nm. Furthermore, wet etchingwas performed by using an aqueous hydrochloric acid solution(HCl:water=1:10) to pattern the amorphous In—Ga—Zn—O.

Next, a source electrode and a drain electrode of a TFT and a lowerelectrode of a light-emitting layer were prepared. A sintered body (witha size of 98 mm in diameter and 5 mm in thickness) having a compositionof ITO (Sn: 5%) was used as a target material. The vacuum reached in thedeposition chamber was 3.0×10⁻⁴ Pa. During the film formation, the totalpressure in the deposition chamber was controlled to the constant valueof 0.3 Pa, Ar gas was flown at 10 sccm, and the distance between thetarget and the film-forming substrate was set at 75 mm. The inputelectric power was RF 300 W, and the film-forming rate was set at 60nm/min. The film thickness was 100 nm. The source electrode, the drainelectrode, and the lower electrode of the light-emitting layer wereformed by patterning at desired positions with a photolithographicprocess and a lift-off process.

Next, on the amorphous oxide semiconductor, a film of SiO_(x) with athickness of 200 nm was stacked using a sputtering process by followingthe same procedure as the formation of the second insulating layer, anda third insulating layer was formed by patterning at desired positionsby means of a photolithographic process and a lift-off process.

Subsequently, a light-emitting layer was formed on the lower electrodefor the light-emitting layer. A hole injection layer was formed of4,4′-bis[N,N-diamino]-4″-phenyl-triphenylamine in a thickness of 45 nmby using a resistive evaporation process. Then, a film of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl was formed thereon in athickness of 25 nm as a hole-transporting layer. Subsequently, a film of4,4′-bis(2,2′-diphenyl vinyl)-1,1′-biphenyl as a light-emitting layerwas formed thereon in a thickness of 30 nm and a film oftris(8-quinolinol) aluminum as an electron-transporting layer wasfurther formed thereon in a thickness of 15 nm, thus completing anorganic EL light-emitting layer as a whole.

Furthermore, an upper electrode of the light-emitting layer was preparedby forming a film of an alloy of Al and Ag in a thickness of 50 nm witha resistive heating evaporation process, and forming an Al film thereonin a thickness of 200 nm. The upper electrode was connected to the drainelectrode of the TFT.

Thereafter, the substrate having the films stacked thereon was sealedwith a glass cap containing a desiccant (not shown), whereby a displayapparatus having basically the same configuration as that shown in FIGS.7A to 7C was produced.

When a desired voltage and signal was given to each of the power supplyline, the GND line, the signal electrode line, and the scanningelectrode line of the above described device to thereby drive the TFTs,a blue light was emitted from the lower surface of the substrate, i.e.,in a bottom emission type. In addition, when the TFTs were driven1,000,000 times, there was not observed any special abnormality in lightemission.

Comparative Example 1

As the present comparative example, a display apparatus was made byfollowing the same procedure as Example 1 with the exception that thesecond insulating layer having a hydrogen content of less than 3×10²¹atoms/cm³ was not used and an interlayer insulating layer was used as agate insulating layer of the TFT. While the TFTs were operated, theoperation was gradually deviated from a normal operation. In the normaloperation, an electric charge should be retained and light emissionshould be observed, while with the display apparatus of the presentcomparative example, a leak current increased with the lapse of time andthe light emission became intermittent.

Example 2

In the next place, Example 2 according to the present invention will bedescribed.

At first, as a substrate, a SiO₂ glass substrate (1737 manufacture byCorning Inc.) was prepared which had an ITO film with a resistivity of1.4×10⁻⁴ Ω·cm and a thickness of 100 nm formed thereon. As thepretreatment before film formation, the substrate was ultrasonicallydegreased and cleaned with acetone, IPA, and ultrapure watersequentially for five minutes each and then dried at 100° C. in air.

Subsequently, a lower electrode of a light-emitting layer was patternedby a photolithographic process and a wet process.

Subsequently, a film with a thickness of 200 nm was deposited by a DCsputtering process using Al—Si (5%) as a target material, and then apower supply line, a GND line, and a signal electrode line werepatterned at desired positions by using a photolithographic process anda dry process. At this time, patterning was performed such that thelower electrode and the power supply line were in contact with eachother.

Next, a film of a-SiNx:H was deposited thereon as an interlayerinsulating layer in a thickness of 700 nm at a substrate temperature of250° C. using a plasma-CVD process. Subsequently, contact holes wereformed in desired positions, and electrodes were embedded so as tocontact the GND line, and the signal electrode line.

Furthermore, films of Ti/Au/Ti were deposited in thicknesses of 5 nm/40nm/5 nm respectively with a DC sputtering process using Au and Ti astarget materials, and a scanning electrode line, two gate electrodes andan electrode for a capacitor were formed at desired positions with aphotolithographic process and a lift-off process.

Thus, a matrix wiring portion and a lower electrode for a light-emittinglayer were formed on the substrate, and then the gate electrode for theTFT and the electrode for the capacitor were formed thereon.

Next, a second insulating layer having a hydrogen content of less than3×10²¹ atoms/cm³ was formed on the substrate having the matrix wiringportion formed thereon. A sintered body (with a size of 98 mm indiameter and 5 mm in thickness) having a composition of SiO₂ was usedfor the target material. A deposition chamber was controlled to reach avacuum degree of 2.0×10⁻⁴ Pa. In the deposition chamber, Ar gas wasflown at 133 Pa for 25 minutes before the film formation, andpre-sputtering was performed for five minutes. During the filmformation, the total pressure in the chamber was controlled to aconstant value of 0.1 Pa, Ar gas was flown at 10 sccm, and the distancebetween the target and the film-forming substrate was set at 75 mm. Theinput power was RF 400 W, and the film forming rate was 7 nm/min. Thedeposited film thickness of the second insulating layer was 220 nm.Furthermore, contact holes were formed in the second insulating layerwith a dry etching process. The dry etching was performed under theconditions of CF₄ gas 20 sccm, 5 Pa, and RF 150 W at an etch rate of 41nm/min for 6.0 minutes.

Next, an amorphous oxide semiconductor was formed as the active layer ofthe TFT. A polycrystal sintered body (with a size of 98 mm in diameterand 5 mm in thickness) having the composition of InGaO₃(ZnO)₄ was usedfor the target material. The sintered body was prepared by dry mixingIn₂O₃, Ga₂O₃ and ZnO (each 4N reagent) as starting materials (solvent:ethanol), followed by presintering (1,000° C.; 2 hours), dry milling,and sintering (1,500° C.; 2 hours). The target had an electricalconductivity of 12 S/cm and was in a semi-insulating state. The vacuumreached in the deposition chamber was 3.0×10⁻⁴ Pa. During the filmformation, the total pressure in the deposition chamber was controlledto a constant value of 0.5 Pa, and the oxygen gas ratio was controlledto 5.5%. In addition, the distance between the target and thefilm-forming substrate was set at 75 mm. The input power was RF 200 W,and the film-forming rate was set at 7.1 nm/min. The deposited filmthickness of the amorphous oxide semiconductor was 35 nm. Furthermore,wet etching was performed by using an aqueous hydrochloric acid solution(HCl:water=1:10) to pattern the amorphous In—Ga—Zn—O.

Next, a source electrode and a drain electrode of the TFT were prepared.Au and Ti were used as target materials and films of Ti/Au/Ti weredeposited in thicknesses of 5 nm/40 nm/5 nm respectively with a DCsputtering process, and the source electrode and the drain electrodewere formed at desired positions with a photolithographic process and alift-off process.

Next, on the amorphous oxide semiconductor, a film of SiO_(x) with athickness of 300 nm was stacked using a sputtering process by followingthe same procedure as the formation of the second insulating layer, anda third insulating layer was formed by patterning at desired positionsby means of a photolithographic process and a lift-off process.

Subsequently, a light-emitting layer was formed on the lower electrodefor the light-emitting layer. A hole injection layer was formed of4,4′-bis[N,N-diamino]-4″-phenyl-triphenylamine in a thickness of 45 nmby using a resistive evaporation process. Then, a film of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl was formed thereon in athickness of 25 nm as a hole-transporting layer. Subsequently, a film of4,4′-bis(2,2′-diphenyl vinyl)-1,1′-biphenyl as a light-emitting layerwas formed thereon in a thickness of 30 nm and a film oftris(8-quinolinol) aluminum as an electron-transporting layer wasfurther formed thereon in a thickness of 15 nm, thus completing anorganic EL light-emitting layer as a whole.

Furthermore, an upper electrode of the light-emitting layer was preparedby forming a film of an alloy of Al and Ag in a thickness of 50 nm witha resistive heating evaporation process, and forming an Al film thereonin a thickness of 200 nm. The upper electrode was connected to the drainelectrode of the TFT.

Thereafter, the substrate having the films stacked thereon was sealedwith a glass cap containing a desiccant (not shown), whereby a displayapparatus having basically the same configuration as that shown in FIGS.9A and 9B was produced.

When a desired voltage and signal was given to each of the power supplyline, the GND line, the signal electrode line, and the scanningelectrode line of the above described device to thereby drive the TFTs,a blue light was emitted from the lower surface of the substrate, i.e.,in a bottom emission type. In addition, when the TFTs were driven1,000,000 times, there was not observed any special abnormality in lightemission.

Comparative Example 2

As the present comparative example, a display apparatus was made byfollowing the same procedure as Example 2 with the exception that thesecond insulating layer having a hydrogen content of less than 3×10²¹atoms/cm³ was not used and an interlayer insulating layer was used as agate insulating layer of the TFT.

When the TFTs were operated, an electric charge was held and lightemission was observed. However, with the lapse of time, a leak currentgradually increased and the light emission became intermittent.

Example 3

In the next place, Example 3 according to the present invention will bedescribed.

In the present example, a display apparatus was made by following thesame procedure as in Example 1 up to the completion of the matrix wiringportion.

Next, a second insulating layer having a hydrogen content of less than3×10²¹ atoms/cm³ was formed on the substrate having the matrix wiringportion formed thereon. A sintered body (with a size of 98 mm indiameter and 5 mm in thickness) having a composition of Si₃N₄ was usedfor the target material. A deposition chamber was controlled to reach avacuum degree of 2.5×10⁻⁴ Pa. In the deposition chamber, Ar gas wasflown at 133 Pa for 20 minutes before the film formation, andpre-sputtering was performed for five minutes. During the filmformation, the total pressure in the chamber was controlled to aconstant value of 0.1 Pa, Ar gas was flown at 15 sccm, and the distancebetween the target and the film-forming substrate was set at 75 mm. Theinput power was RF 400 W, and the film forming rate was 6 nm/min. Thedeposited film thickness of the second insulating layer was 200 nm.Furthermore, contact holes were formed in the second insulating layerwith a dry etching process. The dry etching was performed under theconditions of CF₄ gas 20 sccm, 5 Pa, and RF 160 W at an etch rate of 41nm/min for 7 minutes.

Next, an amorphous oxide semiconductor was formed as the active layer ofthe TFT. A polycrystal sintered body (with a size of 98 mm in diameterand 5 mm in thickness) having the composition of InGaO₃(ZnO)₄ was usedfor the target material. The sintered body was prepared by dry mixingIn₂O₃, Ga₂O₃ and ZnO (each 4N reagent) as starting materials (solvent:ethanol), followed by presintering (1,000° C.; 2 hours), dry milling,and sintering (1,500° C.; 2 hours). The target had an electricalconductivity of 12 S/cm and was in a semi-insulating state. The vacuumreached in the deposition chamber was 3.0×10⁻⁴ Pa. During the filmformation, the total pressure in the deposition chamber was controlledto a constant value of 0.5 Pa, and the oxygen gas ratio was controlledto 5%. In addition, the distance between the target and the film-formingsubstrate was set at 75 mm. The input power was RF 200 W, and thefilm-forming rate was set at 7.1 nm/min. The deposited film thickness ofthe amorphous oxide semiconductor was 30 nm. Furthermore, wet etchingwas performed by using an aqueous hydrochloric acid solution(HCl:water=1:10) to pattern the amorphous In—Ga—Zn—O.

Thereafter, the subsequent process was performed by following the sameprocedure as in Example 1, a display apparatus having basically the sameconfiguration as that shown in FIGS. 7A to 7C was produced.

When a desired voltage and signal was given to each of the power supplyline, the GND line, the signal electrode line, and the scanningelectrode line of the above described device to thereby drive the TFTs,a blue light was emitted from the lower surface of the substrate, i.e.,in a bottom emission type. In addition, when the TFTs were driven1,000,000 times, there was not observed any special abnormality in lightemission.

Example 4

In the next place, Example 4 according to the present invention will bedescribed.

In the present example, a display apparatus was made by following thesame procedure as in Example 2 up to the completion of the matrix wiringportion.

Next, a second insulating layer having a hydrogen content of less than3×10²¹ atoms/cm³ was formed on the substrate having the matrix wiringportion formed thereon. A sintered body (with a size of 98 mm indiameter and 5 mm in thickness) having a composition of Si₃N₄ was usedfor the target material. A deposition chamber was controlled to reach avacuum degree of 2.5×10⁻⁴ Pa. In the deposition chamber, Ar gas wasflown at 133 Pa for 20 minutes before the film formation, andpre-sputtering was performed for five minutes. During the filmformation, the total pressure in the chamber was controlled to aconstant value of 0.1 Pa, Ar gas was flown at 20 sccm, O₂ gas was flownat 3 sccm, and the distance between the target and the film-formingsubstrate was set at 75 mm. The input power was RF 420 W, and the filmforming rate was 6 nm/min. The deposited film thickness of the secondinsulating layer was 200 nm. Furthermore, contact holes were formed inthe second insulating layer with a dry etching process. The dry etchingwas performed under the conditions of CF₄ gas 20 sccm, 5 Pa, and RF 180W at an etch rate of 32 nm/min for 7 minutes.

Next, an amorphous oxide semiconductor was formed as the active layer ofthe TFT. A polycrystal sintered body (with a size of 98 mm in diameterand 5 mm in thickness) having the composition of InGaO₃(ZnO)₄ was usedfor the target material. The sintered body was prepared by dry mixingIn₂O₃, Ga₂O₃ and ZnO (each 4N reagent) as starting materials (solvent:ethanol), followed by presintering (1,000° C.; 2 hours), dry milling,and sintering (1,500° C.; 2 hours). The target had an electricalconductivity of 12 S/cm and was in a semi-insulating state. The vacuumreached in the deposition chamber was 3.0×10⁻⁴ Pa. During the filmformation, the total pressure in the deposition chamber was controlledto a constant value of 0.5 Pa, and the oxygen gas ratio was controlledto 5.5%. In addition, the distance between the target and thefilm-forming substrate was set at 75 mm. The input power was RF 220 W,and the film-forming rate was set at 7.1 nm/min. The deposited filmthickness of the amorphous oxide semiconductor was 30 nm. Furthermore,wet etching was performed by using an aqueous hydrochloric acid solution(HCl:water=1:10) to pattern the amorphous In—Ga—Zn—O.

Thereafter, the subsequent process was performed by following the sameprocedure as in Example 2, a display apparatus having basically the sameconfiguration as that shown in FIGS. 9A and 9B was produced.

When a desired voltage and signal was given to each of the power supplyline, the GND line, the signal electrode line, and the scanningelectrode line of the above described device to thereby drive the TFTs,a blue light was emitted from the lower surface of the substrate, i.e.,in a bottom emission type. In addition, when the TFTs were driven1,000,000 times, there was not observed any special abnormality in lightemission.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2006-328307, filed Dec. 5, 2006, which is hereby incorporated byreference herein in its entirety.

1.-9. (canceled)
 10. A transistor comprising: a source terminal and adrain terminal; an active layer comprising an oxide containing In; agate electrode; and a gate insulating layer between the gate electrodeand the active layer, wherein at least a part of the active layer isamorphous, wherein an electric current flowing between the sourceterminal and the drain terminal of the transistor is less than 10 μAwhen the transistor is in an off state, and wherein the gate insulatinglayer contains hydrogen in an amount of less than 3×10²¹ atoms/cm³. 11.The transistor according to claim 10, wherein the gate insulating layeris disposed between the active layer and a first insulating layer havinga higher hydrogen content than the hydrogen content of the gateinsulating layer.
 12. The transistor according to claim 11, wherein thefirst insulating layer comprises at least one selected from a groupconsisting of silicon oxide, silicon nitride, and silicon nitride oxide.13. The transistor according to claim 10, further comprising a sourceelectrode and a drain electrode which are in contact with the activelayer, wherein the active layer comprises a first portion and a secondportion, wherein the second portion is in contact with the sourceelectrode and the drain electrode, and wherein the first portion is incontact with a second insulating layer.
 14. The transistor according toclaim 13, wherein the second insulating layer contains hydrogen in anamount of less than 3×10²¹ atoms/cm³.
 15. The transistor according toclaim 10, wherein the gate insulating layer comprises at least oneselected from a group consisting of aluminum oxide, yttrium oxide,hafnium oxide, silicon oxide, and silicon nitride.
 16. The transistoraccording to claim 10, wherein the active layer further comprises Zn andGa.
 17. A display apparatus comprising: a plurality pixels, with eachpixel comprising: a display element; a transistor for driving thedisplay element, with the transistor comprising: a source terminal and adrain terminal; an active layer comprising an oxide containing In; asource electrode and a drain electrode electrically connected to theactive layer; and a gate electrode overlapped with a channel portion ofthe active layer; and a first insulating layer in contact with theactive layer, wherein at least a part of the active layer is amorphous,wherein an electric current flowing between the source terminal and thedrain terminal of the transistor is less than 10 μA when the transistoris in an off state, and wherein the first insulating layer containshydrogen in an amount of less than 3×10²¹ atoms/cm³.
 18. The displayapparatus according to claim 17, wherein the first insulating layer isdisposed between the active layer and a second insulating layer having ahigher hydrogen content than the hydrogen content of the firstinsulating layer.
 19. The display apparatus according to claim 18,wherein the second insulating layer comprises at least one selected froma group consisting of silicon oxide, silicon nitride, and siliconnitride oxide.
 20. The display apparatus according to claim 17, whereinthe first insulating layer is a gate insulating layer, and wherein thegate insulating layer is between the active layer and the gateelectrode.
 21. The display apparatus according to claim 20, wherein thegate insulating layer comprises at least one selected from a groupconsisting of aluminum oxide, yttrium oxide, hafnium oxide, siliconoxide, and silicon nitride.
 22. The display apparatus according to claim20, further comprising a source electrode and a drain electrode whichare in contact with the active layer, wherein the active layer comprisesa first portion and a second portion, wherein the second portion is incontact with the source electrode and the drain electrode, and whereinthe first portion is in contact with a third insulating layer.
 23. Thedisplay apparatus according to claim 22, wherein the third insulatinglayer contains hydrogen in an amount of less than 3×10²¹ atoms/cm³. 24.The display apparatus according to claim 17, further comprising a gateinsulating layer, wherein the active layer is between the gateinsulating layer and the first insulating layer.
 25. The displayapparatus according to claim 17, wherein the active layer furthercomprises Zn and Ga.
 26. The display apparatus according to claim 17,wherein the display apparatus is an organic EL display.